1. Field of the Invention
This invention relates to eddy current instrumentation used for non-destructive flaw detection testing and, more particularly, to distinguishing in such testing noise or other undesirable signals from a signal indicating a flaw.
2. Description of the Prior Art
Commercially available eddy current instrumentation is available for use in non-destructive flaw detection testing. Examples of such instrumentation are Models 730-I and 730-II made by K. J. Law Associates, Inc., 26325 West Eight Mile Road, Detroit, Mich. 48240.
In such testing relative motion is commonly established between a self-comparison differential probe and the material under test. Each time such a probe passes over a flaw in the material, a signal is generated by the probe.
The signal generated in response to a flaw typically has a dual polarity characteristic waveform comprising a negative excursion leading a positive excursion, a frequency related to the relative speed between the material (or flaw) and the probe, and an amplitude related to the size of the flaw.
In its commercially available form, the eddy current test instrumentation indicates a flaw whenever it receives from the probe a signal exceeding a predetermined threshold. This threshold is related to and can be adjusted for the nominal minimum flaw size to be detected.
A problem with such instrumentation is that noise signals will frequently exceed the threshold necessary for adequate flow resolution with the result that flaws are incorrectly indicated and parts or materials are unnecessarily rejected.